1. Field of the Invention
The present invention relates to apparatus for cooling optical devices and, more particularly, to an apparatus for controlling coolant flow within an internally cooled optical device.
2. Description of the Prior Art
Optical devices designed for use with high-energy radiation, such as laser optics and monochromators for X-rays, often require cooling to alleviate the adverse effects of severe thermal buildup that occurs from the absorption of high energy radiation. Excessive thermal buildup can result in thermal distortion of the optical device, which may be caused by material expansion per se, or bending resulting from uneven expansion of the materials of the optical device due to temperature gradients.
In order to alleviate these difficulties, various systems have been developed for cooling such optical devices. An accepted way for cooling these devices is through the use of internal cooling, wherein the optical device is mounted on a cooling manifold for distributing a coolant in proximity to the optical device for providing the required cooling. In order to enhance the cooling efficiency, a typically turbulent coolant flow was desired.
An optical device generally comprises an optical faceplate having an exposed surface for receiving the required radiation. In most instances, the cooled surface of the faceplate material lies within 0.1 mm to 1.0 mm of the exposed faceplate surface; therefore, any extra thickness of the faceplate over the 0.1 to 1.0 mm range is considered to be excess and may be needed only for structural purposes. In order to provide the most efficient cooling possible, the active material should be in close proximity to the coolant; therefore, it is desirable that the faceplate be made as thin as possible.
While it is desirable to have a thin faceplate, this desirable characteristic results in additional problems, in that the thin faceplate is structurally weak and therefore may be adversely affected by the pressure and flow characteristics of the coolant. High coolant pressures can result in high spatial frequency bowing or bending of the faceplate (hydraulic ripple). A turbulent flow of the coolant can generate vibrations in the faceplate. Any displacement or movement of the faceplate surface will distort the resulting image or data.
It has become customary in the art to provide very small cooling channels, which are generally referred to as micro-channels, along the surface of a coolant manifold, with said surface being covered by the faceplate, so that the faceplate essentially forms one wall of the cooling channels. This structure provides the beneficial result that the coolant is in direct contact with the faceplate material, but again subjects the faceplate to coolant pressure and vibration due to turbulent coolant flow.
Most prior art devices have either paid little attention to controlling the flow to each cooling channel, or have micro-managed the flow such that each cooling channel has its own inlet and outlet and flow control means. The former approach results in a simple design but rather uneven cooling that can result in unacceptable thermal distortions in the optical device. The latter approach is extremely complicated, requiring flow control for each micro-channel, resulting in excessively high cost.